In order to find the proper Clerget divisor, P—P' is multiplied by the normality fraction of the original solution, i. e., 1/2, 2/5, or 1/5. From table 19, National Bureau of Standards Scientific Paper $375, page 189, under the column marked "75 ml X 4/3" and opposite the value of P-P' (reduced by the normality fraction), find the value of the Clerget divisor. Apply the temperature correction and divide into P-P'1. The pipetting of solutions shall be done with great care. The pipettes must be kept scrupulously clean by frequent use of a bichromate sulfuric acid cleaning mixture, the lead being first removed with alkaline tartrate solution. During delivery it shall be held in a vertical position and allowed to drain by gravity for the definite length of time specified by the calibration. It is advisable to perform the direct and invert polarizations for each analysis during the same series of observations, placing the tubes side by side and feeding the water jackets from the same source. The hydrochloric acid (d 20°/4°, 1.1029) is made by diluting the concentrated cp acid by approximately an equal volume of water. It is sufficiently accurate to adjust the diluted solution to a density of 24.9 Brix at 20.0° C. The Determination of reducing sugars in cane sirups and molasses.-The method for the determination of the reducing sugars in cane sirups and molasses containing approximately 50 percent total sugars shall be as follows: Eight grams of molasses are transferred to a 500-ml flask, dissolved, clarified with a minimum quantity of normal lead acetate solution and made to volume and filtered. filtrate is freed from excess of lead by the addition of dry potassium oxalate. Aliquot portions of 50 ml of the lead-free filtrate are taken for analysis. Transfer 25 ml each of solutions A and B of the Soxhlet reagent to a 400-ml beaker and add 50 ml of the above solution. Heat the beaker upon an asbestos gauze over a Bunsen burner, so regulating the flame that boiling begins in 4 minutes and continues boiling for exactly 2 minutes. Keep the beaker covered with a watch glass throughout the entire time of heating. Without diluting, filter the cuprous oxide at once on a Gooch crucible, using suction. Wash the cuprous oxide thoroughly with water at a temperature of about 60° C, then with 10 ml of alcohol, and dry for 15 minutes in an oven at 100° C. Ignite crucible for 10 minutes over a Bunsen burner. The precipitate is reduced to metallic copper in methyl alcohol vapors. This is done by placing about 15 ml of methyl alcohol in a 400 ml beaker, placing a triangle support in the beaker so the top is above the level of the alcohol. Heat covered beaker to boiling on hot plate; remove cover and place hot Gooch crucible on triangle. This ignites the alcohol vapors. Immediately cover with watch glass and allow to remain for about 6 minutes, remove, dry in an oven at 100° C for about 5 minutes, cool in desiccator, and weigh. The amount of reducing sugar corresponding to this weight of copper is found from table 78, p. 564 (column marked "0.4 g total sugar"). Control determinations should be carried out, using standard dextrose. In the event that the percentage of total sugars in the molasses varies appreciably from 50 percent, such a weight is taken for the reducing-sugar determination, that 50 ml of the solution will contain 0.4 or 0.3 g total sugar to conform to the specifications of the method of Munson and Walker. Example.--In a sirup containing 80 percent of total sugars, 5 g of the sample are dissolved and made up to 500 ml, and 50-ml portions taken for analysis, each such portion containing 0.5 g of sample or 0.4 g of total sugars. Determination of sucrose and raffinose in beet molasses.-The method for the determination of the sucrose and raffinose in beet molasses shall be as follows: Prepare a solution of the beet molasses containing 65 g in 500 ml (half normal). Make to volume at the temperature at which the polariscopic observations are to be made. Clarify with the minimum quantity of Horne's dry basic lead acetate and shake thoroughly. Filter. Direct polarization.--Polarize the solution to obtain the direct reading and correct first for zero point displacement and then correct to the value which would have been obtained if 26 g of the sample were taken in 100 ml of solution, (P). Invert polarization.-Pipette 75 ml of the clear filtrate into a 100-ml flask, add 10 ml of HCl (d 20°/4°, 1.1029). Immerse in a water bath which is maintained at 70° C. Agitate continually for 3 minutes and allow to remain in the bath for a total time of 10 minutes. Cool quickly and make up to volume at the temperature at which the observations are to be made. Shake and filter as rapidly as possible. Polarize. Correct first for zero-point displacement, and then correct to the value which would have been obtained if 26 g of the sample were taken in 100 ml of solution (P'). 1 See also p. 155. All polarizations shall be made in water-jacketed tubes provided with tubulature and thermometer. Substitute these values of P and P' in the following equation: (.5142+.00196 (t − 20)) P— P' S= .8413.00320 (t-20) (145) Substitute the value of S and the value of P in eq. 146 and solve to find the percentage of raffinose: Determination of reducing sugars in beet molasses.-The method for the determination of reducing sugars in beet molasses shall be as follows: For the determination of reducing sugars in a molasses containing approximately 50 percent of total sugars, 20 g of the beet molasses are transferred to a 250-ml flask, dissolved, clarified with the minimum quantity of normal lead acetate, made to volume, and filtered. The clear filtrate is freed from the excess of lead with dry potassium oxalate. Taking aliquot portions of 50 ml of the lead-free filtrate, the reducing sugars are determined as described under "cane molasses." Find the amount of reducing sugars corresponding to the weight of copper obtained from table 78, p. 564 (column marked "2 g total sugars"). In the event that the percentage of total sugars in the beet molasses varies appreciably from 50 percent, such a weight is taken that 50 ml of the solution will contain 2 g of total sugars. Determination of weight per gallon of molasses. A special 100-ml volumetric flask with a neck of approximately 8-mm inside diameter shall be used. Weigh the flask empty and then fill it with molasses, using a long-stemmed funnel reaching below the graduation mark, until the level of the molasses is up to the lower end of the neck of the flask. The flow of molasses may be stopped by inserting a glass rod of suitable size into the funnel so as to close the stem opening. Remove the funnel carefully to prevent molasses coming in contact with the neck, and weigh flask and molasses. Add water almost up to the graduation mark, running the water down the side of the neck to prevent mixing with the molasses. Allow to stand for several hours or overnight to permit the escape of bubbles. Place the flask in a constant-temperature water bath, preferably at 20° C, for a sufficient time for it to reach the temperature of the bath, then make to volume at that temperature, with water. Weigh. Reduce the weight of the molasses to vacuo and calculate the density. From table 117, page 644, convert to weight per gallon in air. Correction for temperature. The temperature of the molasses shall be determined at the time of gauging. The weight per gallon of the molasses shall be corrected to this temperature, using as the factor for the cubical expansion of molasses 0.00043 per unit volume per degree centigrade. The weight per gallon at the temperature of gauging is therefore W2 = W1 (147) where t1 = temperature of determination, W2 weight per gallon at temperature, t2, W1 weight per gallon at temperature, t1. Moisture determination.For the determination of moisture in sugars, dry approximately 4 g in a metal dish of a diameter of 55 mm and a height of 15 mm. Each sample shall be subjected to a temperature of 100° C for 2 hours, care being exercised that the dishes are not in close proximity to the heaters. 49 An example of the calculation is given on page 252 of this Circular. 323414-42-52 |